Surface and electrochemical study of DBSA-doped polypyrrole films grown on stainless steel

Electrically conducting polypyrrole films doped with dodecylbenzenesulphonic acid (PPy-DBSA) have been electrochemically polymerized on stainless steel. The surface and electrochemical properties of the films were investigated by a combination of cyclic voltammetry (CV), scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). The CV results showed an irreversible reaction of electropolymerization. All PPy-DBSA films had a nodular or cauliflower-like surface morphology. The grain size was dependent on the growth current density and the growth time. The ratio of incorporated DBSA anions to pyrrole repeat units in the films was similar to1:2. The doping level, calculated from the positive charge accumulated in the polymer chain (at.% ratio (N+ + N2+)/N-total), varied as a function of the growth current density and the growth time. The maximum doping level occurred at a growth current density of 0.5 mA cm(-2), consistent with an oxidation peak of the pyrrole monomer observed by CV. The interfacial layer between the polymer and substrate was also studied. A sulphur-rich layer was observed, indicating the presence of a thin layer of DBSA at the interface. In addition, iron was detected on the metal side of the film as a result of its dissolution from the stainless-steel electrode during the electropolymerization process. These results have implications for the use of polypyrrole films as environmentally friendly corrosion mitigants. Copyright (C) 2002 John Wiley Sons, Ltd.